The invention relates to a method of determining whether the writer of a sign is the same as the writer of a previously written sign.
Credit or cash card transactions rely on either, or both the visual comparison of a submitted signature with that on the card or the use of a Personal Identity Number (PIN). For a number of reasons, these do not provide a particularly secure means of identification.
The signature written during a transaction is often given minimal, if any, comparison with that existing on the card, while the signature on the card may also be forged. PIN numbers are often not remembered and may be stored by the user in such a way that the illegal acquisition of the card will also reveal the PIN number.
In view of these problems, there is a desire for some method of automatic sign, particularly signature, verification which does not rely on a simple visual comparison and which also allows for the use of unattended, automatic transaction apparatus. An important performance parameter in any such application is that the acceptance of valid signatures should be high (preferably greater than 99%), requiring that any verification system should accept day to day variations of genuine signs. In the case of credit or cash cards, any non-confirmation of a signature results in a referal to the card company which is expensive.
In one prior proposal described in IBM Technical Disclosure Bulletin Vol. 21, No. 1 June 1978 a system is described in which a user initially supplies six sample signatures which are stored in a data bank. Subsequent signatures are compared with the six stored signatures. If a successful comparison cannot be made then provision is made to change, under supervision, the stored signatures so that they more closely reflect the changes than have occurred in the person's signature since the original signatures were recorded. Such systems are expensive because they rely on the combination of an on-line connection to a host computer, an inbuilt system data base, and some method of recording prerecorded signatures.
These techniques are not feasible for an off-line system which incorporates no data base.
GB-A-1480066 illustrates a verification system in which if a first signature cannot be verified the user is given the opportunity of providing a second signature which is processed in a similar way. If this signature also cannot be verified then the signatory is rejected. A modification of this method in which parameters setting the limits for acceptance may be updated is disclosed in GB-A-2104698. Both these prior art methods are very simple in form and rely solely on repeating the verification procedure independently on two different signatures.
A far more sophisticated verification system is described in IBM Technical Disclosure Bulletin Vol 24. No. 2 of July 1981. This provides for the inputting of up to four repeat signatures and carries out various complex comparison steps. The problem with this system is that it is very undesirable to require a signer, particularly a genuine signer, to repeat his signature up to four times.